Neutrophil secretory vesicles are the intracellular reservoir for GPI-80, a protein with adhesion-regulating...

The subcellular localization of GPI-80, a novel, adhesion-regulating protein, was investigated in human neutrophils. Surface expression of GPI-80 was determined by FACS analysis as well as by the ability for phospholipase C to cleave the protein from the cell surface. Increasing amounts of GPI-80 were exposed on the cell surface after weak stimulation with the chemoattractant fMLF, suggesting that the protein can be translocated to the plasma membrane from intracellular stores. By subcellular fractionation of the neutrophils, GPI-80 was defined as a component of a light membrane fraction, containing secretory vesicles and plasma membranes, and it was absent from the neutrophil granule fractions. Separation of the plasma membranes from the secretory vesicles by flotation gradient fractionation confirmed that the GPI-80 was localized in the mobilizable secretory vesicles by approximately 50%, and the rest was plasma membrane-bound. Thus, we identify secretory vesicles as the reservoir of GPI-80 from which it may translocate to the plasma membrane after weak stimulation of the cells.